An apparatus of this kind has been known from the post-doctoral thesis by K. ALBERT entitled "NMR Flow Spectroscopy, Contributions to its Development and Application", Chemical and Pharmaceutical Faculty of the Eberhard-Karls University in Tubingen, 1988, pages 75 to 77. This known measuring apparatus is used in the biomedical field for carrying out perfusion measurements on the liver of a rat. The metabolic processes are observed in an NMR flow measuring cell, using the NMR measuring method.
An NMR measuring circuit and a liver circuit are interconnected via a chamber which is designed as balancing vessel. In addition to the blood to be investigated, which is pumped from the liver of the rat into the balancing vessel using a pump, a mixture of oxygen and CO.sub.2 is fed into the balancing vessel.
The known measuring permitted allowed the enzyme activity of the liver to be determined by NMR measurement.
However, it is a disadvantage of the known measuring apparatus that the path between the chamber serving as balancing vessel and the location of the NMR measurement is very long and predetermined in a fixed way. Thus, it is not possible, with the aid of the known method, to release a reaction in a reaction chamber, i.e. at a defined place, in at least one reagent in such a way that the reagent can be examined, by nuclear magnetic resonance spectrometry, continuously and yet after an individually preselectable, in particular very short, period of time after the commencement of that reaction.
It is, therefore, desirable to have the possibility to predetermine a chemical and/or physical reaction in a very defined way, as regards its location and time, and to be able in addition to examine the reaction product, by nuclear magnetic resonance spectrometry, continuously and yet after an individually preselectable, in particular a very short, period of time after the commencement of that reaction.
Further, it is desirable to subject the reaction product and/or the reagent or the reagents supplied to the reaction chamber to a long premagnetization period in the highest possible magnetic field.
This is desirable because in the case of NMR measurements transitions between nuclear energy levels split in the magnetic field are excited by an irradiated RF field. Splitting is proportional to the magnetic field strength. When in thermal equilibrium, the levels are populated according to the Boltzmann distribution law, i.e. the population difference between two nuclear energy levels is proportional to the quotient of the magnetic field strength and the temperature, it being possible to develop the exponential function of the Boltzmann distribution law, and the linear term being sufficient. Thus, the higher the magnetic field at a predetermined temperature, the greater the population difference which in its turn determines the measuring sensitivity. However, the thermal equilibrium is not established immediately, the development over time being determined by the relaxation time T.sub.1 which usually is in the order of a few seconds.
Now, when a reagent flows from an area of decaying field strength (equal population) into the area of the magnetic field of the NMR spectrometer, the population difference approaches the new value of equilibrium only asymptotically at the time constant T.sub.1. This leads to the result that when the relaxation times T.sub.1 are relatively long and the reaction paths or reaction times are relatively short, the population difference corresponding to the field acting in the NMR measuring cell will not have been established in the latter, i.e. that measuring sensitivity will be lost. Sufficient premagnetizations can be achieved also with short preselectable reaction times. Basically, it is of no consequence in this connection if the magnetization is carried out before or after the commencement of the reaction. Of course, it is desirable that the premagnetization field be as high as possible.
Now, it is the object of the present invention to improve an apparatus of the type described above in such a way as to optimize the conditions for recording chemical and/or physical reaction sequences by nuclear magnetic resonance spectrometry, and to allow an arrangement of the reaction path which is flexible as regards the reaction conditions and favorable as regards the premagnetization time.